For 10.7 to 12..1.3 upgrade, you have to first upgrade to 11.5.10, then upgrade to 12.1.1 then apply 12.1.3 maintenance pack.
Upgrading Oracle Applications (zipped)
Oracle E-Business Suite Upgrade Guide Release 11i to 12.1.1
For generating .fmb files from .fmx, this is not possible.
Thanks for Reply and Information.
I have another question. As I told we are using 10.7 version EBS, which developed with 4.5 Version forms, 2.5 version reports and 8i DB version. is it possible to upgrade only forms from 4.5 to 10g, reports from 2.5 to 10g and 8i DB to latest version DB without following general Oracle Apps upgradation process? I mean we just open the 4.5 version .fmb with 10g form builder, will do syntax related changes and will put it back into server. If we do like above (like general d2k application upgradation steps) will our 10.7 version EBS will work?
Kindly let me know if you need any more clarification.
If FMB's gets compiled successfully post changes it should work.